Method of preserving a rubber which comprises treating the rubber with a solid resinous aralkylated dihydroquinoline antioxidant



Patented fJec. 29, 1953 2,664,407 METHOD OF PRESERVIN G A RUBBER WHICH COMPRISES TREATING THE RUBBER WITH A SOLID RESINOUS ARALKYLATED DIHYDROQUINOLINE AN TIOXIDAN T Joseph R. Ingram, Nitro, W. Va., assignor to Monsanto Chemical Comp poration of Delaware any, St. Louis, Mo., a cor- N Drawing. Application November 24, 1948, Serial No. 61,911

3 Claims. (Cl. 260-4) This invention relates to the art of preserving rubber and particularly to antioxidants and flex improving agents for the compounding of rub,- ber and to the rubber compositions obtained thereby.

It has been found in accordance with the present invention that aralkylated 1,2-dihydroquinoline bodies are a highly effective and economical class of rubber antioxidants. The new antioxidants are obtained by reacting a 1,2-dihydroquinoline with a suitable aralkylating agent and are to be distinguished from alkyl, aryl, and other substituted dihydroquinolines known. to possess antioxidant properties. Thus substituted dihydroquinoline antioxidants have been obtained by reacting a substituted aniline with a. ketone but these products do not possess the properties of the new class. The new antioxidants are not only adaptable to vulcanizates containing carbon black for improving flexing properties but are suitable for white stocks also. In contrast to most antioxidants containing nitrogen, they are resistant to staining and discoloration.

Aralkyl substituted 1,2-dihydroquinolines may be prepared conveniently by a number of methods, for example, by condensing an aralkyl halide with a 1,2-dihydroquinoline in the presence of a catalyst such as aluminum chloride or zinc chloride. Suitable halides phenyl methyl chloride, ride, phenethyl chloride, chlor propyl benzene, indanyl chloride, and the like. Another method of preparation is to react an aromatic substituted olefinic hydrocarbon with a 1,2-dihydroquinoline in the presence of a non-oxidizing catalyst. Among the aromatic substituted olefinic hydrocarbons which will readily react are styrene, o-, m-, and p-methyl styrene, o-, m-, and p-ethyl styrene, the diethyl styrenes, allyl benzene, the divinyl benzenes, the phenyl butadienes, a and ,3 vinyl naphthalene, vinyl pyridine, indene, a methyl indene, and their hydroxy and alkoxy substituted analogues. Mixtures of the above materials are also contemplated.

The chemical structure of the products obtained by reacting a 1,2-dihydroquinoline with an aralkyl halide or an aromatic substituted olefinic hydrocarbon is not known but the reaction is believed to involve, principally, the carbon atom containing the halogen substituent of the aralkyl halide or the unsaturated carbon atom nearest the aromatic nucleus of the aromatic substituted olefinic hydrocarbon and a carbon atom in the nucleus of the dihydroquinoline.

triphenyl methyl chloare benzyl chloride, di-

However, the

present invention is not limited to any assumption as to chemical structure but pertains broadly to the products obtained by reacting an aralkyl halide or an aromatic substituted olefinic hydrocarbon with a 1,2-dihydroquinoline.

As exemplary of the preparation of the new antioxidants the following examples are illustrative and are not to be constructed as limitative thereof.

Example 1 To a 3-neck flask equipped with a thermometer, a stirrer, and a reflux condenser, containing 34.6 parts by Weight (substantially 0.2 mol) of 2,2,4-trimethyl 1,2-dihydroquinoline was added 27.6 parts by Weight (substantially 0.2 mol) of indene and 75 ml. of benzene. While agitating, 26.6 parts by weight (substantially 0.2 mol) of anhydrous aluminum chloride was added. The mixture was then heated at the reflux temperature for 4 hours. The mix was cooled and. placed in a distilling apparatus containing 130' parts by weight of a 25% sodium hydroxide solution and the benzene distilled oil. Thereupon the mix was steam distilled to remove the last traces of benzene and unreacted indene. The residue was washed free of alkali and dried at 60 C. The dried product believed to be an indanyl substituted 2,2,4-trimethyl 1,2-dihydroquinoline was found to have a melting point of approximately C. The yield was about Example 2 To a B-neck flask equipped with a thermometer, a stirrer, and a reflux condenser containing 17.3 parts by weight (substantially 0.1 mol) of 2,2,4-trimethyl 1,2-dihydroquinoline was added 10.4 parts by weight (substantially 0.1 mol) of styrene. While agitating, 13.3 parts by weight (substantially 0.1 mol) of aluminum chloride was added. The reaction vessel was then placed in a steam bath and heated for 24/ hours. A solid resinous material developed which was washed with water and caustic, and taken up with toluene. Upon removal of the solvent 26.5 parts (96% yield) by weight of a resinous product was recovered.

Example 3 To a suitable reaction vessel containing 26 parts by weight (substantially 0.15 mol) of 2,2,4- trimethyl 1,2-dihydroquinoline and 22.2 parts by weight (substantially 0.15 mol) of anethole (pmethoxy allyl benzene) was added 20 parts by weight (substantially 0.15 mol) of aluminum chloride. The contents of the reaction vessel were heated for 3 hours at 60 to 80 C. Upon 3 cooling the reaction product was washed with water and caustic and taken up with benzene, Upon removal of the solvent 39 grams (80% yield) of a resinous like product having a melting point of about 80 C. was obtained.

Example 4 A mixture of 38 parts by weight, (substantially 0.3 mol) of benzyl chloride,.52 parts by weight (substantially 0.3 mol) of 2,2,4trimethyl l,2-dihydroquinoline, and 50 parts by weight (substantially 0.36 mol) of anhydrous zinc, chloride was heated over a steam bath for-7' hours. The zinc chloride catalyst was removed from the reaction product by several washings with hot water. Thereupon the resinous product was taken up with benzene and washed free of residual acid. Upon removal of the solvent approximately 68 parts by weight (about 100% yield) of a resinous product was obtained.

Example 5 A suitable reaction vessel containing a reaction mix consisting of 47 parts by weight (substantially 0.3 .mol) of indanyl chloride and 51.9 parts byweight (substantially 0.3 mol) of 2,2,4:- trimethyl 1,2-dihydroquinoline dissolved in carbon disulfide was heated for 2 hours at approximately 40-46 weight (substantially 0.3 mol) of anhydrous aluminum chloride. The carbon disulfide was removed and the reaction product was washed with water and caustic, and taken up with benzene. Upon removal of the solvent 80 parts by weight of a resinous product was isolated. This product was not unlike the residual product of Example I.

Example 6 A mixture of. 54.6 partsby weight (substantially 0.7 moi) of benzene and 30.8 parts by weight (substantially 0.2 mol) of carbon tetrachloride was placed in a S-neck flask equipped with an agitator, a thermometer, and a reflux condenser and thereto was added slowly 26.7 parts by weight (substantially 0.2 mol) of anhydrous aluminum chloride. 3M5 parts by weight (substantially 0.2 mol) of 2,2,4-trimethyl LZ-dihydroquinoline dissolved in parts by Weight (substantially 0.38 mol) of benzene was admitted to the reaction vessel and the contents heated for 2 hours at the reflux temperature. Upon cooling the reaction product was washed with water anad caustic and the residual benzene distilled off leaving 74 parts by weight (95% yield) of a reddish yellow resinous product believed to be principally triphenyl methyl substituted 2,2,4-trimethyl 1,2-dihydroquinoline. The resinous product was distilled under diminished pressure and the residue found to have a melting point of about 93 C.

While. in the above examples only one dihydroquinoline reactant has been described, other 1,2-dihydroquinolines, mixtures of dihydroquinolines, and the crude reaction product of 1 mol of an aromatic amine. and 2 mole of an aliphatic ketone, can be aralkylated in a like manner to produce similar products having useful oxidative inhibiting and nondiscoloring properties. For example, 2-methy1-2A-diethyl-1,2-dihydroquinoline, 2emethyl-2,4-diisopropyl1,2-dihydroquinoline, and the crude reaction product of lrnol of aniline and 2 mole of acetone are contemplated.

As specific embodiments of the invention portraying the age-resistant properties of aralkyl C. in the presence of parts by Carbon black Zinc oxide substituted 1,2-dihydroquinolines, rubber stocks were compounded comprising a Parts by weight Smoked sheets rubber.

Stcaric aci pro uct Styrene-2, 2, 4-trimethyl 1, 2-dihydroquinoline reaction prod- 110i Anethole-2, 2, 4-trimethyl 1, 2 dihydroquinoline r e a ct io 11 product l l 1 The rubber stocks so compounded were vulcanized in a press for 60 and 90 minutes respectively at 135 C. Test strips were cut from the vulcanized stocks and artificially aged for 6 and 9 hours respectively at 121 C. in an air bomb under pounds per square inch pressure. The results are as follows:

Table I Tensile in p. s. i. 1 Modulus in Ultiafter aging in p. s; i. Ult. mate air bomb at elong., tensile 121 C. 1 7 percent in 1 p. s. i. 300% i 500% 6 hrs. 9 hrs. 00 min. cure at Stock A. 1,820 3,803 590 4, 650 3,047 1, 670 Stock 13.... l, 793 3,813 593 4, 620 3, 167 1,853 Stock 0...- 1 863 3, 827 590 4, 073 3, 097 1, 070 Stock D 1, 827 3, 973 517 4 150 1,710 783 min. cure at Stock A... 1,923 4, 070 533 4, 360 2, 077 1, 427 2,120 4, 047 573 4, 550 3,025 1,203 4,177 527 4,400 3,157 1,430 4, 227 1 510 4,313 1,695 055 The foregoing data clearly show that the various stocks treated with aralkylated 1,2-dihydroquinolines possess excellent age-resistant properties as compared to the control stock (stock D). Compounded stocksA, B, and C exhibited excellentanti flex cracking properties, as for example the following results were obtained employing a fiexing machine as set forth by L. V. Cooper, Analytical Edition of Industrial and Engineering Chemistry, vol. 2, No. 4, pp. 391-394.

Table II Kilocycles to failure Stock A B C D Unaged 168 203 107 138 Aged 0 hours at 121 C. in air bomb 4 184 128 101 25 Aged 120 hours at 70- 91 1 Qinoxygen bomb. 55 '78 l As exemplary of the non discoloring properties of the new antioxidants, the following stock was compounded:

Parts by weight Pale crepe rubber Zinc oxide 60 Lithopone 20 Sulfur 2 Benzothiazyl thio' benzoate 0.675

Diphenylguanidine-phthalic acid reaction product 0.825 Paraffin 0.25 Styrene-2,2,4-trimethyl-1,2-dihydroquinoline reaction product 1.0

and vulcanized in a press for 45 and 60 minutes respectively at 126 C. After 9 hour air bomb aging at 121 C. and 80 pounds per square inch pressure, the tensile strengths for the 45 and 60 minute cures, respectively, were 2840 and 2820 pounds per square inch. Test strips cut from the 45 and 60 minute cured rubber stock showed only a slight yellowing effect after exposure to the 1,2-dihydroquinolines such as the anethole- 2,2,4-trimethyl 1,2 dihydroquinoline reaction product, the triphenyl methyl chloride-2,2,4-trimethyl-1,2-dihydroquinoline reaction product and the benzyl chlor de-2,2,4-trimethyl-1,2-dihydroquinoline reaction product similarly exhibited remarkable resistance to light deterioration upon exposure to sunlamp rays.

Obviously the examples set forth above show that rubber compositions containing an aralkylated 1,2-dihydroquinolne are markedly resistant to the deteriorating influences of flexing, heat, oxidation, and light, and while the above data describes only specific compounds of the new class of rubber antioxidants, all members of said class are advantageous in carrying out the objects of the invent-on.

For most purposes 1 per cent of the new antioxidants based upon the weight of the rubber af- Amounts above 1 percent, as for example 2.5 percent or more, may be employed where desired although usually Without added benefit.

By the term rubber as employed in the specification and appended claims, unless otherwise modified, is intended to be used in its generic sense to include rubber substitutes, natural rubher, synthetic rubber, and the like whether or not admixed with fillers, pigments, accelerators, etc.

By the term treating as employed in the appended claims is intended to be used in a generic sense to include the incorporation of the antioxidant into a rubber or rubber like substance by milling or mastication, its addition to rubber latices, and any equivalent procedure such as applying it to the surface of a vulcanized or unvulcanized rubber in the form of a powder or paste.

While certain specific embodiments of this invention have been described in detail herein, it is to be understood that the invention is not limited for many modifications may be resorted to such as varying the proportion of the new anti-oxidants and incorporating in the stock other vulcanization accelerators than the above disclosed, without departing from the spirit or scope of the invention.

What is claimed is:

l. The method of preserving a rubber which comprises treating the rubber with a solid resinous aralkylated dihydroquinoline antioxidant compostion obtained by heating in the presence of one mole of a catalyst from the group consisting of aluminum chloride and zinc chloride one mole of 2,2,4-trimethyl-1,2-dihydroquino1ine and substantially one mole of a reagent selected from the group consisting of phenyl substituted methyl chlorides, substituted solely by phenyl groups, indanyl chloride and v-nyl substituted aromatic compounds of the benzene and naphthalene series containing at least one but not more than two CH2=CH groups as the sole olefinic constituents.

2. The method of preserving a rubber which comprises treating the rubber with a solid resin ous aralkylated dihydroquinoline ant oxidant composition obtained by heating in the presence of one mole of a catalyst from the group consisting of aluminum chloride and zinc chloride one mole of 2,2,4-trimethyl-1,2-dihydroquinoline and substantially one mole of styrene.

3. The method of preserving a rubber which comprises treating the rubber with a solid resinous aralkylated dihydroquinoline antioxidant composition obtained by heating in the presence of one mole of a catalyst from the group consisting of aluminum chloride and zinc chloride one mole of 2,2,4-trimethyl-1,2-dihydroquinoline and substantially one mole of benzyl chloride.

JOSEPH R. INGRAM.

OTHER REFERENCES Berichte, v01. of 1932, page 1515. 

1. THE METHOD OF PRESERVING A RUBBER WHICH COMPRISES TREATING THE RUBBER WITH A SOLID RESINOUS ARALKYLATED DIHYDROQUINOLINE ANTIOXIDANT COMPOSITION OBTAINED BY HEATING IN THE PRESENCE OF ONE MOLE OF A CATALYST FROM THE GROUP CONSISTING OF ALUMINUM CHLORIDE AND ZINC CHLORIDE ONE MOLE OF 2,2,4-TRIMETHYL-1,2-DIHYDROQUINOLINE AND SUBSTANTIALLY ONE MOLE OF A REAGENT SELECTED FROM THE GROUP CONSISTING OF PHENYL SUBSTITUTED METHYL CHLORIDES, SUBSTITUTED SOLELY BY PHENYL GROUPS, INDANYL CHLORIDE AND VINYL SUBSTITUTED AROMATIC COMPOUNDS OF THE BENZENE AND NAPHTHALENE SERIES CONTAINING AT LEAST ONE BUT NOT MORE THAN TWO CH2=CH- GROUPS AS THE SOLE OLEFINIC CONSTITUENTS. 